Heretofore, as one example of techniques in this field, for example, Patent Document 1 listed below discloses the technique that a ring gear is press-fitted to an outer circumferential surface of a flange of a differential case, and after that, both ends of the ring gear are swaged or deformed at both ends of the flange so as to fix the ring gear. Then, predetermined components as well as the ring gear are assembled to the case, and thereby a differential sub assembly used for a power transmission mechanism of a vehicle is obtained.